Mid-infrared spectrometer attachment to light microscopes

ABSTRACT

A mid-infrared (mid-IR) spectrometer attachment performs reflection spectroscopy measurements using commercially available infinity corrected light microscopes. The mid-IR spectrometer attachment introduces infrared radiation into the optical path of a visible light microscope. Radiation from the mid-IR spectrometer source is directed by a radiation director to a mid-IR objective lens affixed to the microscope nosepiece. The objective lens focuses the radiation on to a subject sample surface in order to acquire either internally or externally reflected infrared spectra by subsequently directing the sample encoded reflected infrared radiation to an infrared radiation detection system. The mid-IR spectrometer attachment is mechanically and optically compatible with a plurality of commercial infinity-corrected visible light microscopes. The visible light optics of the microscope can be used for visual imaging but mid-IR objective lenses are needed for infrared spectral analyses at wavelengths greater than about 4 micrometers. A sample-defining mask, which is part of the spectrometer system, can be made adjustable and a trichroic element used as the radiation directing means can allow for simultaneous viewing and infrared measurement of a microscopic sample. In one embodiment, the trichroic element is designed to be a reflector in the mid-IR region (reflectivity of around 95%) while being a beam splitter in the near infrared (near-IR) region and transparent in the visible region, thereby providing the opportunity to observe near-IR radiation from the sample that originated from the infrared source using commercially available video cameras while simultaneously collecting mid-IR radiation for spectroscopic analysis. In another embodiment, the trichroic element is designed to be a reflector in the mid-IR region (reflectivity of around 95%) while being a beam splitter in both the near-IR the visible regions, thereby allowing a visible illumination means to be incorporated in the attachment, and thus eliminating the need for a separate vertical visible light illuminator.

FIELD OF THE INVENTION

[0001] The present invention relates generally to the field ofmid-infrared (mid-IR) spectrometry, and more specifically to anattachment to infinity-corrected, commercially available lightmicroscopes to provide the techniques of internal and externalreflection infrared microspectrometry.

BACKGROUND OF THE INVENTION

[0002] Spectroscopic analysis using radiant energy in the infraredregion of the electromagnetic radiation spectrum is a primary techniquefor chemical analysis of molecular compounds. The infrared spectralregion extends from 0.7 to 250-micrometers, however the mid-IR region isgenerally considered to cover the region from about 2.5 to about25-micrometers (or parts thereof), which is commonly used for molecularvibrational spectroscopy. While the primary distinction between near-IRand mid-IR regions is based upon whether the underlying molecularfrequencies are fundamental or overtone frequencies, instrumentcomponents tend to differ and also be specific by region. There is someoverlap however, and specifically mid-IR Fourier transform infraredspectrometers typically cover that part of the near-IR region from 1 to2.5 micrometers.

[0003] This invention defines an attachment apparatus and method forinfrared spectroscopic or radiometric analysis of microscopic samples ofsolids or liquids, including biological materials, combining external orinternal reflection spectroscopy with visible light and near-IR radiantenergy viewing of microscopic samples by using an attachment to standardcommercially available visible light microscopes and commerciallyavailable video cameras. The magnification optics for infrared spectralanalysis are infrared transmitting objective lenses that are used tofocus a beam of radiant energy onto a sample, or sample surface, collectthe reflected radiant energy, and present that energy to a detectorsystem for spectral analysis.

[0004] Since the introduction of commercial infrared microspectrometers,the advantage of combining the capabilities of a visible-lightmicroscope with an infrared spectrometer has been of great importance.Infrared microscopes, such as those disclosed in U.S. Pat. No. 4,877,747(the '747 patent) issued to Donald W. Sting and Robert G. Messerschmidt,have been used for an ever-expanding range of applications. Thesespecialized microscopes were attached to commercial Fourier transforminfrared (FT-IR) spectrometers. Such microscope/FT-IR systems have beenused to detect and identify trace contaminants, to analyze multilayeredcomposites, micro-electronic devices, phase distributions in polymericmaterials, inclusions in minerals, abnormal cellular materials, DNA, andnumerous other materials.

[0005] Heretofore, all known combinations of mid-IR spectrometers andvisible light microscopes were composed of (1) a combination of ageneral purpose laboratory spectrometer and an attachment to thespectrometer having visible light illumination and viewing, or (2) aspecially designed integrated instrument combining infrared spectroscopyand visible imaging features. In all cases, the resulting productsemphasized the infrared spectroscopy capability, utilizing visiblemicroscopy capabilities as a means to support the infrared spectroscopycapability.

[0006] Known special infrared microscope systems and attachments tomid-IR spectrometers have become pervasive even though such systems andattachments are costly and complex. The microscope attachments tolaboratory FT-IR spectrometers, described in the '747 patent to Stingand Messerschmidt, among others, have become the standard configurationsfor infrared microspectroscopy systems. These complex microscopeattachments typically provide both transmission and reflectioncapabilities and use variable remote-image-plane masks to define sampleareas for infrared analysis. All of this known art, however, consists ofspecial purpose FT-IR microscopes with specialized optical systems thatare appended to large bench-top spectrometers, or fully integrated FT-IRmicroscope systems using some visible light microscope components. Nosuch systems known use an attachment to visible light microscopes, as iscontemplated by our invention.

[0007] Our invention provides for the use of both external-reflectionand internal-reflection microspectoscopy techniques. Internal-reflectionmicrospectroscopy provides certain advantages over both transmission andexternal reflection microspectroscopy, particularly in the ability toanalyze thick samples. With the introduction of internal-reflectionmicrospectrometry, as shown in U.S. Pat. No. 5,093,580 to Donald W.Sting, and U.S. Pat. No. 5,200,609 to Donald W. Sting and John A.Reffier (also known as attenuated total reflection microspectrometry ormicro-ATR) reflection microspectrometry has gained ever-greaterimportance. Furthermore, our invention extends the capabilities ofinternal-reflection microspectroscopy by using the unique ATR technologydisclosed in U.S. Pat. Nos. 5,703,366 and 5,552,604 issued to Sting andMilosevic to create a novel infinity-corrected ATR objective used formicrospectroscopy.

[0008] All previous forms of infrared microspectroscopy apparatus weredesigned from the perspective of the spectroscopist, whereas thisinvention is designed from the perspective of those using visible lightmicroscopes. Our invention treats the infrared spectroscopy capabilityas an adjunct to a visible light microscope, and thereby providesextension of the visible microscope's capabilities. It is a primaryobject of the present invention to provide an FT-IR spectrometerattachment that is easily attached to a commercially available lightmicroscope without compromising any of the available visible lightmicroscope features, options, and capabilities.

SUMMARY OF THE INVENTION

[0009] The present invention provides an optical system, apparatus andmethod to use a mid-IR spectrometer system as an attachment tocommercial light microscopes for molecular analysis of materials. Inthis invention a small spectrometer, in combination with optical,mechanical and electronic components, form an apparatus that can bedirectly attached to a light microscope for measurement of infraredspectra of microscopic samples or sample domains. Because it can bereadily attached directly to existing microscopes, using conventionalmechanical connectors that are typically used for microscopes, costs aresignificantly lower than the current art method of using a dedicatedinfrared microscope that is attached to a laboratory FT-IR spectrometer.Furthermore, because of the ease of use and accessibility of such lowcost infrared spectroscopy capability to material scientists,biologists, and pathologists, as well as others using conventionalvisible light microscopes, it is expected that significantinterdisciplinary benefits will occur.

[0010] Using our invention, infrared spectra are acquired using eitherthe external-reflection or the internal-reflection spectroscopytechnique. By using reflection spectroscopy techniques, nearly all typesof samples can be analyzed. A thin film of material for example, can bemounted on an infrared reflective, but visibly transmissive, substratesuch as low-E glass to be analyzed by reflection-absorption, a specialcase of external-reflection, whereby infrared radiation from thespectrometer is directed onto and through the sample film to the low-Eglass substrate, where the radiation is reflected and subsequentlypasses through the film a second time, whereupon the radiationultimately is directed to a detector for analysis. An absorptionspectrum is thereby acquired, but the measurement was made using theexternal-reflection technique. For external-reflection spectroscopy, theexternal-reflection infrared objective lens does not contact the sample,as it must with the ATR objective lens which is used forinternal-reflection spectroscopy.

[0011] Any thick or thin sample that is placed in contact with theinternal-reflection element of an ATR objective lens can result in anATR spectrum. Because the infrared spectrum of most samples can bemeasured by using either internally or externally reflected radiation,the infrared spectrometer attachment can provide molecular analyses in asimple and economical manner.

[0012] Another object is to use infinity-corrected reflecting objectivesand complementary optical components both to direct radiant energy ontoa microscopic area and to allow visualization of the magnified image ofthe specimen and of a highly correlated measure of the mid-IR radiation,the near-IR radiation from the infrared source, through an integralvideo system. Visualization of the mid-IR radiation is achieved bybringing together three distinctly separate ideas in a novel way. First,infrared spectrometers, and specifically mid-IR FT-IR spectrometers,provide a source of infrared radiation that includes some near-IRradiation. Second, commercially available video camera arrays aresensitive to near-IR radiation. Finally, commercially available opticalelements are readily made that transmit or reflect radiation differentlyfor different wavelength regions. Using these facts in a novel waycaused us to define a new term, a “trichroic” element, meaning anoptical element with defined functions in three different wavelengthregions. For example, in the preferred embodiment of the mid-IRattachment, the trichroic element largely transmits visible lightradiation, it both transmits and reflects near-ir radiation, and itlargely reflects mid-IR radiation. The specifics of how the trichroicelement is used in conjunction with the preferred embodiment isdiscussed in detail when describing FIGS. 7 and 8. Using this novel ideaand others has allowed us to incorporate the mid-IR spectrometerattachment into infinity-corrected light microscopes to provide uniqueand significant benefits to the microscopist. In all embodiments, theinclusion of the mid-IR attachment on the microscope maintains a simpleoptical system without compromising any of the standard features andcapabilities of the light microscope.

[0013] A still further object of the present invention is to provide asimplified system for detecting contact of a sample with an internalreflection element. Observing physical contact with visible light is adirect indication of optical contact in the mid-IR region since visibleregion wavelengths are shorter than mid-IR region wave lengths. That is,if contact is achieved at a shorter distance (less than a quarter of avisible wavelength) it must be achieved for the longer mid-IR regionwavelengths.

[0014] One embodiment of the invention provides an optical system, whichmeets the Koehler illumination criterion of focusing the source elementof the radiation at the pupil (aperture) of the objective lens. Visiblelight illumination systems typically meet this criterion, and thisembodiment of our invention meets the Koehler illumination criterion forboth visible and infrared radiation. To our knowledge, infraredmicrospectrometer systems have never before been designed to meet theKoehler illumination criterion. This embodiment of our invention, whichmeets this criterion, we believe, will be of increasing importance toinfrared microspectrometry as infrared array detectors become morereadily available at affordable prices.

[0015] Other objects of this invention will be apparent from thefollowing description, which is provided to enable any person skilled inthe art to make and use the invention, and which sets forth the bestmode contemplated by the inventors of carrying out their invention.Various modifications to the specific embodiment disclosed herein,within the general principles of the invention as defined herein, willbe apparent to those skilled in the art.

DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a side schematic of a commercially available visiblelight microscope.

[0017]FIG. 2 is a top elevation schematic of the mid-IR attachment ofthe present invention.

[0018]FIG. 3 is a side elevation schematic of the mid-IR attachment ofthe present invention.

[0019]FIG. 4 is a side elevation schematic of the mid-IR attachment ofthe present invention mounted on a commercially available visible lightmicroscope equipped with an objective for internal reflection spectralmeasurements.

[0020]FIG. 5 is a top elevation schematic of the mid-IR attachment ofthe present invention wherein the mid-IR spectrometer source includes asample defining mask.

[0021]FIG. 6 is a top elevation schematic of the mid-IR attachment ofthe present invention wherein a visible light illuminator along withsample and aperture defining masks is included.

[0022]FIG. 7a, 7 b, and 7 c are respectively illustrative of how thetrichroic element functions for visible light, mid-IR radiation, andnear-IR radiation

[0023]FIG. 8 illustrates reflectance vs. wavelength for visible light,near-IR and mid-IR.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0024] Turning now in more detail to the invention, and initially toFIG. 1, a commercially available infinity corrected visible lightmicroscope is schematically shown as 1. Said microscope is generallycomposed of a frame 2, a sample support stage 3, transmitted visiblelight source 4 a and/or a reflected visible light source 4 b, nosepiece5, infinity corrected objective lens 6, and visible light viewing means,such as a binocular or trinocular viewer with eyepieces 7.

[0025] All of the optical elements are aligned to the visible lightoptical path 8 of the microscope 1. A sample 9 is typically placed on asample substrate 10, which is supported by the sample support stage 3.The sample support stage 3 typically has adjustments to provide forthree dimensional spatial movements to place the sample 9 or someattribute of the sample 9 at the focus of the infinity correctedobjective lens 6 so that observation by the visible light viewing means7 is readily effected.

[0026] For samples that are transparent or translucent, the transmittedvisible light source 4 a can be used to provide sample illumination inconjunction with condenser 12. In that case, the visible light beam istransmitted from visible light source 4 a along the visible lightmicroscope optical centerline 8 through the condenser 12, the samplesubstrate 10, then through the sample 9 and the objective lens 6. Fromobjective lens 6, the visible light continues along optical centerline 8and finally to the visible viewing means 7.

[0027] Samples that are visibly opaque might require that the reflectedvisible light source 4 b to be used to illuminate the sample. In thatcase, visible light from illuminator 4 b is introduced along themicroscope optical path 8 via a visible beam splitter, which directslight downward to the objective lens 6, which focuses the light onto thesurface of the visibly opaque sample 9. Some light is reflected by thesurface of sample 9 and collected by the objective lens 6, whichcollimates the reflected visible light and directs it back to thebeamsplitter of visible illuminator 4 b, whereby some of the visiblelight is transmitted through the beamsplitter to the visible lightviewing means 7.

[0028] In addition, certain samples might require special illuminationtechniques such as polarized light or radiation of specific frequenciesto create florescence or other special visible effects. In such cases,visible light sources 4 a or 4 b might be readily replaced with suchspecial illumination means, as is known in the art.

[0029] Commercially available microscope systems provide for significantflexibility and capabilities, the present invention adds the capabilityof mid-IR microspectroscopy without degrading those flexibilities andcapabilities.

[0030]FIG. 2 schematically displays a top view of the preferredembodiment of the present invention, shown generally by 100. The mid-IRspectrometer attachment 100 includes the mid-IR spectrometer source 101,which provides a source of infrared radiation 102 directed towardradiation directing means, or radiation director 103, which is atrichroic element in the preferred embodiment. Radiation director 103provides the means to couple and align the source of infrared radiation102 with the visible optical path 8 of the microscope 1, as shown inFIG. 4. Radiation director 103 reflects infrared radiation 102 such thatit is aligned with the optical centerline 8 of the microscope 1 forinteraction with a sample via an infinity corrected infrared objectivelens 6 (see FIG. 4). After interaction with the sample 9, that has beenmanipulated by the stage 3 (see FIG. 4) adjustments to be at the focusof the infrared objective 6, infrared radiation 102 that is now sampleencoded is collected by objective lens 6 and returned along themicroscope optical path 8, whereby it is reflected a second time byradiation director 103 to the infrared detector system 104. Infrareddetector system 104 is composed of directing and focusing mirrors 104 a,detector 104 b, and detector electronics 104 c that are commonly used inthe art. Directing and focusing mirrors 104 a can be a single mirror ormultiple mirrors, largely depending upon the physical space constraintsimposed by the size and shapes of microscope components. Detector 104 bis typically a high sensitivity cooled MCT detector as is standardpractice for infrared microscopes, however, any high sensitivitydetector with sufficient broadband width is acceptable. Increasingly,multi-element infrared detectors are being used for infraredmicrospectroscopy, and we contemplate using multi-element (ormulti-pixel) detectors to provide spatial spectroscopic images ofsamples. Specifically, FIG. 6 discloses a mid-IR attachment opticalconfiguration intended to have the special benefit of nearly constantinfrared radiation density at the sample 9 when using a multi-elementdetector 104 b. Such constant radiation density at the sample 9minimizes spectral artifacts resulting from different elements pixels)of the detector being at significantly different radiation levels. Allof the mid-IR spectrometer attachment 100 components are affixed to aframe 105, which provides for a cover 106 (see FIG. 3) to accommodate apurged environment for the infrared radiation 102.

[0031]FIG. 3 displays the present invention, showing the variouselements, 101 through 106 as they might schematically appear in a sideview relative to the microscope optical path 8. Male flange 107 andfemale flange 108 are complementary to each other and mate tocomplementary mechanical details on the visible illuminator 4 b and thevisible viewing means 7 as assembled in FIG. 4. Adjustment screws 109 infemale flange detail 108 are used to center the viewing means 7 ontooptical centerline 8. Likewise, adjustment screws (not shown) on thevisible illuminator 4 b provide for alignment of the attachment 100 tothe optical centerline 8 of the microscope. Such alignment forconcentricity is well known and practiced by those in the art, and isthereby not discussed in detail.

[0032]FIG. 4 schematically displays a side view of the presentinvention, shown in a usable position with a commercially availableinfinity corrected visible light microscope. In this figure, bothvisible light sources 4 a and 4 b are shown, however the presence of 4 aor 4 b is dependent only on the visible illumination requirements of thesample being observed and thereby both are not jointly required for thepresent invention. For many situations, visible illuminator 4 b is notrequired, thereby allowing attachment 100 to be attached directly toframe 2. Furthermore, an infinity corrected mid-IR objective lens 6 isshown in the nosepiece 5. It is common practice to use nosepieces thataccommodate multiple objective lenses; a single objective lens is shownonly for simplicity.

[0033] The mid-IR spectrometer attachment 100 is shown in place on ageneric commercial light microscope 1 with both a transmitted lightilluminator and a reflected light illuminator 4 b. Since there areseveral manufacturers and designs of microscopes, the mechanicalfixtures that couple the mid-IR spectrometer attachment 100 to themicroscope 1 might vary. The only requirements for the microscope 1 arethat it is able to use infinity corrected objectives, and there are noglass elements between the mid-IR spectrometer attachment 100 and thenosepiece 5.

[0034] Furthermore, while the reflected light visible source 4 b isshown to be below the mid-IR spectrometer attachment 100 of the presentinvention, with slight modification the reflected visible light source 4b can be placed above the mid-IR spectrometer attachment 100 withoutcompromising the spirit of the invention.

[0035] In addition, a video camera 11 is shown, attached to the visiblelight viewing means 7 to provide for electronic viewing of the sampleand/or sample matrix. While such video camera 11 is used in aconventional way to observe a sample, etc., it is furthermore used in anovel, unique way to view the near-IR radiation from the infraredspectrometer source 101. Since the near-IR radiation and the mid-IRradiation are co-mingled as infrared radiation 102, observing thenear-IR radiation is a direct measure of the mid-IR radiation, which isnot observable by the video camera 11. Commercially available videocameras 11 are typically solid-state video cameras, and some are ChargeCoupled Devices, or CCD cameras, although our invention will work withany video camera that is sensitive to near-IR radiation, and/or mid-IRradiation. When used as a mass consumer market video camera, thesecameras typically have filters for blocking near-IR radiation that mustbe removed for our use. An example of such a commercially availablevideo camera, or CCD camera is CBCAmerica Model No. CMH512-L12 that issensitive to near-IR radiation. It is used to provide an electronicsignal for visual light representation of the near-IR radiation from theinfrared spectrometer source. In the absence of visible radiation, weare able to observe the location and extent of the mid-IR spectrometersource radiation by observing the near-IR radiation, which is commingledwith the mid-IR radiation. The net effect is that we are able to observethe extent of the mid-IR spectrometer radiation as it interacts with thesample or specific areas of the sample. To those skilled in the art,this is an extremely important feature since it provides directobservation as to what is being spectroscopically measured.

[0036] Such direct observation significantly simplifies the analysisprocess and assures that “what you see is what you analyze”. Since theinfrared detector 104 b will detect all infrared radiation that is inits field of view, it is sometimes necessary to restrict the source ofthe infrared radiation 102 to be contained within the boundaries of thesample of interest. Such use of sample defining masks is well known inthe art and thereby is not described in detail herein. In our invention,in order to achieve more specificity, one sample defining mask 101 c,along with optics 101 b and 101 d are used as shown in FIG. 5 as part ofthe mid-IR spectrometer source 101. When used in conjunction with aradiation director 103, such as a trichroic element that will be furtherexplained below, and a video camera 11, ample confirmation of “what yousee is what you analyze” is provided.

[0037] Furthermore, infrared alignment and optical system confirmationis made dramatically easier with the video camera 11. First, the camera11 is aligned to the microscope 1 with attachment 100, for example asshown in FIG. 4, using visible light means 4 a and/or 4 b. The radiationdirecting means 103 and the other optical components of attachment 100are then adjusted using visible light to grossly align the attachment100. Then, by switching the visible light source off and leaving theinfrared source on, and observing (with the video camera 11) near-IRradiation that is commingled with mid-IR radiation, the attachment 100is finely adjusted, again using adjustments (not shown) on radiationdirecting means 103 and the other optical components of attachment 100.

[0038]FIG. 5 displays a top elevation schematic of the mid-IR attachment100 of the present invention, including a sample defining mask 101 c,wherein the infrared beam 102 is focused by mirror lens 101 b at thesample defining mask 101 c and re-collimated by mirror lens 101 d anddirected to radiation director 103. The mid-IR spectrometer source 101is herein defined to include mirror lenses 101 b and 101 d, and sampledefining mask 101 c.

[0039]FIG. 6 displays a top elevation schematic of the mid-IR attachment100 of the present invention wherein a visible light source 101 m, isincorporated into the mid-IR attachment 100 of the present invention inorder to eliminate the need for and associated cost of a separatevisible illumination means 4 b. Both the infrared radiation 102 and thevisible light beam 101 n are subsequently focused, masked twice, andrefocused and re-collimated to achieve the criterion of Koehlerillumination for both infrared radiation and visible light illumination.

[0040] In the figure, infrared radiation 102 and visible lightillumination 101 n from visible light source 101 m are commingled at atrichroic element 101 e and made to follow the same optical path 102.The trichroic element 101 e is designed to largely reflect mid-IRradiation and near-IR radiation, while largely transmitting visiblelight 101 n.

[0041] The commingled visible and infrared radiation, now referred to as102, is focused by mirror lens 101 f to the aperture defining mask 101g, and through sample defining mask 101 h, and on to mirror lens 101 jwhich simultaneously creates an image at infinity of all the radiationat sample defining mask 101 h and an image of the radiation at mask 101g at the aperture of the infinity corrected objective lens 6, once ithas been reflected by flat mirror 101 k and radiation director 103. Forthis configuration, as shown in FIG. 6, trichroic element 103 is adifferent trichroic element than that of the configurations shown inFIGS. 2 and 5, and is designed to largely reflect mid-IR radiation andto act as a beamsplitter for near-IR radiation and visible light.

[0042] The mid-IR spectrometer source 101 in this embodiment is hereindefined to include spectrometer 101 a, trichroic element 101 e,condensing mirror 101 f, radiation mask 101 g, sample defining mask 101h, lens mirror 101 j, directing mirror 101 k, visible light source 101m, along with the associated visible light path 101 n and the infraredlight path 102 commingled with 101 n.

[0043] In addition to the cost benefit associated with eliminatingvisible light source 4 b, there are benefits associated with microscopealignment and instrument integrity assurance. Furthermore, with theavailability of multi-element mid-IR array detectors, it is significantthat the Koehler criterion be met in order to insure evenly distributedinfrared illumination of the sample and subsequently the detector, fornon-absorbing samples.

[0044] Referring now to FIG. 7, please note the trichroic element 103 isan optical filter element that has three distinct functions. It issubstantially transparent to visible light (FIG. 7a) and thereby allowsthe visible light microscope 1 to operate in a normal fashion (see FIGS.7 and 8). A sample can be illuminated from either above (see FIG. 4),using visible illuminator 4 b, or below, using illuminator 4 a, allowingthe sample 9 to be observed by the visible light viewing means 7 (seeFIG. 7a). For mid-infrared radiation (FIG. 7b), the trichroic element103 is highly reflective and behaves like a mirror. For example,depending on the composition and thickness of the layers making up thetrichroic element 103, reflectivity in the mid-infrared can be as muchas 95% or more (see FIG. 8). Radiation 102 from the infraredspectrometer source 101 is reflected by the trichroic element 103 towardthe microscopic objective 6. The radiation reflects off the sample 9 ora reflective substrate 10 under the sample 9, back through reflectingobjective 6, and back to trichroic element 103. It then makes a secondreflection at the trichroic element 103 and is directed to the mid-IRdetector system 104, composed of additional optics 104 a and 104 b anddetector 104 c. In the near infrared the trichroic element 103 behaveslike a beamsplitter, as depicted in FIG. 7c. The near infrared radiationfrom the source 101 travels along the identical path as the mid-infraredradiation, commingled in the infrared radiation 102. When it arrives atthe trichroic element 103, some radiation is reflected to objective 6 inthe same way as the mid infrared radiation. The rest passes through andis not used. The objective 6 directs radiation to reflect off the sample9 or a reflective substrate 10 under the sample 9, and back through thereflecting objective 6, and on to trichroic element 103, whereat some ofthe near-IR radiation is reflected to the infrared detector system 104and some passes through the trichroic element 103 and on to the visibleviewing means 7, which incorporates video camera 11.

[0045] The radiation that passes through the trichroic element 103 isdetected by video camera 11, which is sensitive to near infraredradiation. The output of the camera can be sent to a monitor for visibleviewing. The radiation could be directed to the eyepieces of visibleviewing means 7, but it is invisible to the human eye. It should benoted although shown in three separate diagrams, all three modes ofoperation occur simultaneously. It will be appreciated by those of skillin the art that, depending on the desired reflectance (FIG. 8) forinfrared and transmittance for visible and near-IR radiation, thecoatings and substrate can be chosen appropriately. For example,reflectance of mid-IR from 80% to 95%, and even up to about 99%, can beachieved. U.S. Pat. No. 5,160,826 to Cohen, et al., which is herebyincorporated by reference in its entirety, discloses a coated windowthat substantially transmits visible radiation while simultaneouslyreflecting infrared radiation. Trichroic elements need to be specifiedby functionality by spectral region and can be ordered from opticalcomponent manufacturers such as Spectral Systems of Fishkill, New York.

[0046] These three functions are novel and important. Transparency ofvisible light allows normal visible microscopy. Reflectivity in themid-infrared allows spectroscopic analysis. Since the near-infraredradiation travels virtually the same path as the mid-infrared radiationfor optical paths with little or no chromatic aberration, it willilluminate an area that coincides with the area of spectroscopicanalysis. Therefore, the camera 11 views the part of the sample 9 thatis being analyzed by the mid-infrared radiation. In addition,simultaneous near-infrared and visible viewing, permit precisepositioning of the sample 9 on the microscopic stage 3 to select thedesired portion of the sample to analyze.

[0047] While the present invention has been illustrated by thedescription of embodiments thereof, and while the embodiments have beendescribed in considerable detail, it is not the intention of theapplicants to restrict or in any way limit the scope of the appendedclaims to such detail. Additional advantages and modifications willreadily appear to those skilled in the art. The invention, in itsbroader aspects, is not limited to the specific details, therepresentative apparatus, and illustrative examples shown and described.Accordingly, departures may be made from such details without departingfrom the spirit or scope of the applicant's general inventive concept.

We claim:
 1. A mid-infrared attachment for an infinity-corrected,visible light microscope for spectroscopic analysis of a sample,comprising: a source of infrared radiation; a radiation director; and aninfrared radiation detection system, wherein said attachment isinsertable into the optical path of the microscope.
 2. The attachment ofclaim 1, wherein said radiation director is a trichroic element, saidtrichroic element capable of reflecting a majority of the mid-infraredradiation, splitting any near-infrared radiation and transmitting amajority of any visible light.
 3. The attachment of claim 1, whereinsaid radiation director is usable for transmitting a majority of visiblelight while reflecting a majority of the infrared radiation.
 4. Theattachment of claim 1 in combination with an infinity-corrected lightmicroscope, said microscope including an infinity-corrected mid-infraredobjective lens.
 5. The attachment of claim 4, wherein the microscopeincludes a frame and a visible light viewing means and the attachment isinsertable into the optical path of the microscope between the frame andthe visible light viewing means.
 6. The attachment of claim 5, whereinsaid radiation director directs said source of infrared radiation tosaid objective lens along the optical path of the microscope.
 7. Theattachment of claim 5, wherein said radiation director directs saidsource of infrared radiation onto said sample resulting in a reflectedsample encoded infrared radiation, said reflected infrared radiationbeing directed to said infrared radiation detection system.
 8. Theattachment of claim 1 wherein said radiation director is a trichroicelement capable of reflecting a majority of the infrared radiation andsplitting any near-infrared radiation and any visible light radiation.9. The attachment of claim 1 wherein said mid-infrared spectrometer is aFourier transform infrared spectrometer.
 10. The attachment of claim 7wherein the attachment is connected to the frame of the microscope. 11.The attachment of claim 7 wherein a video camera is mounted on theattachment for viewing near-IR radiation reflected off the sample.
 12. Aspectrometer attachment for an infinity corrected visible lightmicroscope for spectroscopic analysis of a sample comprising: a sourceof mid-IR radiation; a visible light source; an optical system tocommingle the mid-IR radiation and visible light along a common opticalpath including a radiation mask and a sample-defining mask; a radiationdirector for directing the mid-IR radiation and visible light along anoptical path of the microscope and a radiation detector for analyzingsample encoded mid-IR radiation returning from the sample.
 13. A sampleanalysis system comprising: an infinity corrected visible lightmicroscope; an attachment to said microscope including a mid-IRradiation source having some near-IR radiation; a radiation director insaid attachment for directing the mid-IR radiation along the opticalpath of the microscope; a radiation detector in the attachment foranalyzing mid-IR radiation reflected from the sample to the radiationdirector to the detector, and; a video camera for viewing reflectednear-IR radiation from the sample, through the radiation director to thevideo camera.
 14. The system of claim 13 wherein said radiation directoris a trichroic element.
 15. The system of claim 14 wherein saidattachment includes a visible light source on an optical system forcommingling the mid-IR radiation and visible light along a commonoptical path.
 16. The system of claim 15 wherein said optical systemincludes a radiation mask and a sample defining mask along the commonoptical path.
 17. The system of claim 14 wherein the trichroic elementis selected for the functionality required for the sample being analyzedand permits simultaneous viewing in visible light, near-infrared, andmid-infrared.